Fabrication and exchange-spring properties of SrFe12O19@Fe3O4 nanocomposites with core-shell structure

SrFe 12 O 19 @Fe 3 O 4 nanocomposites with core–shell structure were synthesized by combining sol–gel and hydrothermal methods. The phase composition, surface morphology, and magnetic properties of the nanocomposites were investigated using X-ray powder diffraction, scanning electron microscopy, Raman spectroscopy and vibrating sample magnetometer. Findings show that the samples comprise two phases and that Fe 3 O 4 particles are coated on the SrFe 12 O 19 particles surface. The average particle size of SrFe 12 O 19 core particles increases from 80 nm to 120 nm as the calcination temperature increased from 850 °C to 950 °C for 2 and 5 h. The coercivity of the SrFe 12 O 19 @Fe 3 O 4 core–shell nanocomposites is smaller than that of the core SrFe 12 O 19 nanoparticles. The hysteresis loops for the SrFe 12 O 19 @Fe 3 O 4 nanocomposite particles shows a typical “bee waist”. The variations in coercivity, saturation magnetization and anisotropy constant of the core–shell nanocomposite samples are attributed to the architecture, phase composition of nanocomposite particles and the fundamental magnetization mechanism as well as the degree of exchange coupling between two magnetic phases. • SrFe 12 O 19 @Fe 3 O 4 core-shell nanocomposite samples obtained via hydrothermal method. • Hard and soft magnetic phases coexist in all the core-shell nanocomposites. • The Fe 3 O 4 particles coated on the SrFe 12 O 19 core surface. • The architecture, phase composition and the degree of exchange coupling were studied. • The coercivity of SF-950 2h reached 90% that of the SrFe 12 O 19 core.